Male homosexuality and maternal immune responsivity to the Y-linked protein NLGN4Y.
Level 4 - case-series / case-control
Case-control comparative biomarker study
PubMed 29229842 · doi:10.1073/pnas.1705895114
What was done
Researchers developed immune assays targeting two Y-linked proteins involved in brain development: protocadherin 11 Y-linked (PCDH11Y) and neuroligin 4 Y-linked (NLGN4Y; isoforms 1 and 2). They analyzed plasma antibody levels against these male-specific proteins in mothers of sons (about half of whom had a gay son), women with no sons, and male controls.
What was found
Women had significantly higher anti-NLGN4Y antibody levels than men. After statistically controlling for the number of pregnancies, mothers of gay sons—particularly those with older brothers—had significantly higher anti-NLGN4Y levels than control groups of women, including mothers of heterosexual sons. The abstract reports no numerical values, concentrations, or effect sizes.
Why it matters
This provides direct serological evidence supporting the maternal immune hypothesis for the fraternal birth order effect in male homosexuality.
Limits
The abstract does not report participant sample sizes (n), exact antibody concentrations, or effect sizes. The observational case-control design establishes an association rather than direct proof of altered fetal neurodevelopment.